Downing Street described the country's behaviour as "politically motivated and totally disproportionate" while Spain threatened to take Britain to the United Nations as diplomatic relations between the two deteriorate.

As planned, the Royal Navy headed south today with one ship calling in at Gibraltar.

Madrid responded by beefing up border controls - leading to lengthy queues - and suggesting a possible €50 (£43.30) fee could be imposed on every vehicle entering or leaving the British territory through the border with Spain.

Downing Street said that any possible legal action would be done through Europe.